The present disclosure relates to a fusing system including a heat storage mechanism. More particularly, the disclosure relates to a fusing system including a fuser roller that includes a heat transport layer having high thermal capacity.
Electrophotographic printing and copying devices typically are provided with fusing systems that serve to thermally fuse a toner image onto a recording medium, such as a sheet of paper. Such fusing systems normally comprise a heated fuser roller and a heated pressure roller that presses against the fuser roller to form a nip in which the fusing occurs. FIG. 1 illustrates a simplified end view of a typical prior art fusing system 100. As indicated in FIG. 1, the fusing system 100 generally comprises a fuser roller 102, a pressure roller 104, internal heating elements 106, and a temperature sensor 108. The fuser and pressure rollers 102 and 104 comprise hollow tubes 110 and 112 that are coated with outer layers 114 and 116 of elastomeric material.
The internal heating elements 106 typically comprise halogen lamps that uniformly irradiate the inner surfaces of the rollers 102 and 104. Through this irradiation, the inner surfaces are heated and this heat diffuses to the outer surfaces of the fuser and pressure rollers 102 and 104 until they reach a temperature sufficient to melt the toner (e.g., approximately between 160xc2x0 C. to 190xc2x0 C.). The fuser roller and the pressure rollers 102 and 104 rotate in opposite directions and are urged together so as to form a nip 118 that compresses the outer layers 114 and 116 of the rollers together. The compression of these layers increases the width of the nip 118, which increases the time that the recording medium resides in the nip. The longer the dwell time in the nip 118, the larger the total energy that the toner and recording medium can absorb to melt the toner. Within the nip 118, the toner is melted and fused to the medium by the pressure exerted on it by the two rollers 102 and 104. After the toner has been fused, the recording medium is typically forwarded to a discharge roller (not shown) that conveys the medium to a discharge tray.
The outer layers 114 and 116 are normally constructed of rubber materials (e.g., silicon rubber) that have high thermal resistance and low thermal capacity. These characteristics can be explained with the thermal model 200 shown in FIG. 2. The thermal model 200 represents the thermal characteristics of the fuser roller 102 shown in FIG. 1 as a recording medium (e.g., sheet of paper) passes through the nip 118. As indicated in FIG. 2, the model 200 comprises a circuit that includes a thermal energy source 202 representative of the internal heating element 106. The energy source 202 delivers a constant amount of energy to a thermal capacitor C1 that is representative of the hollow tube 110 of the fuser roller 102. The energy provided by the energy source 202 must overcome the thermal resistance provided by the resistor R1, which represents the outer layer 114. Due to the large thermal resistance of the materials used to construct the outer layer 114, the resistance provided by R1 is very large. In addition, the energy from the source 202 must overcome the thermal resistance of the resistor R2, which represents heat loss due to convection. This energy also reaches a second thermal capacitor C2 representative of the thermal capacitance of the outer layer 110. Due to the low thermal capacity of materials used to construct the outer layer 114, the thermal capacitance of C2 is very small. Finally, the energy encounters the thermal resistance of resistor RL, which represents the thermal load of the recording medium that passes through the nip 118. Heat generated by the passage of the energy through the resistor RL is represented by xe2x80x9c+xe2x80x9d and xe2x80x9cxe2x88x92xe2x80x9d in FIG. 2.
As will be appreciated by persons having ordinary skill in the art, the large resistance of the resistor R1 poses an impediment to the transfer of energy from the interior of the fuser roller 102 to the fuser roller outer surface of the outer layer 114. This impediment creates the heat transport delay which is the primary cause of delay in the warming of the fusing system 100. In addition, the small thermal capacity of capacitor C2 means that the outer layer 114 can store little energy. Because of this fact, the energy stored within the outer layer 114 is quickly dissipated as recording media are passed through the nip 118.
In addition to increasing the warm-up time of the fusing system 100, use of conventional fusing systems such as that shown in FIG. 1 can also result in gloss variation along the length of the recording media. As is known in the art, gloss variation relates to the phenomenon in which the gloss of the fused toner changes over the length of the recording medium. This variation is due to the fact that the fuser roller 102 typically has a circumference which is smaller than the length of the recording medium. Therefore, the fuser roller 102 will normally pass through several revolutions as the recording medium passes through the nip 118. Due to the transfer of heat to the medium through each revolution and to the fact that the outer layer 114 cannot store large amounts of thermal energy, the temperature of the outer surface of the fuser roller 102 can drop significantly from the leading edge of the medium to its trailing edge. This can result in the printed recording medium having a first section adjacent its leading edge in which the printed media is highly glossy, a second section at its middle where the printed media has a less glossy finish, and a third section adjacent its trailing edge in which the printed media has a non-glossy (i.e., matte) finish.
Gloss variation is undesirable for several reasons. First, printed materials having gloss variation are unaesthetic in that the printed media have an inconsistent appearance. This is particularly true in the case of color printing or photocopying in that the glossy portions of the printed media will appear more vibrant than less glossy portions. Second, a glossy finish normally indicates better fusing to the recording medium. With good fusing, there will be better adhesion between the toner and the recording medium and therefore less chance of the toner flaking off of the recording medium.
From the foregoing, it can be appreciated that it would be desirable to have a fusing system that avoids one or more of the disadvantages described above associated with conventional fusing systems such as gloss variation.
The present disclosure relates to a fusing system for fusing toner to a recording medium. The fusing system comprises a fuser roller including an elastomeric layer and a heat transport layer disposed around the elastomeric layer, the heat transport layer having high thermal capacity, and a pressure roller in contact with the fuser roller.
The present disclosure also relates to a fusing method that helps reduce gloss variation of printed media fused to a recording medium with a fusing system. The method comprises the steps of forming a heat transport layer having high thermal capacity at an outer surface of a fuser roller of the fusing system, heating the heat transport layer, and transferring heat from the heat transport layer to the recording medium as it passes through a nip of the fusing system.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.